**Core Concept**
The patient is diagnosed with an ectopic pregnancy, a life-threatening condition where the fertilized ovum implants outside the uterus, most commonly in the fallopian tubes. The primary goal of treatment is to prevent maternal mortality and morbidity while preserving future fertility.

**Why the Correct Answer is Right**
The standard treatment for ectopic pregnancy is medical management with methotrexate (MTX), a folate antagonist that inhibits dihydrofolate reductase (DHFR) enzyme, leading to DNA synthesis and cell division arrest in rapidly dividing cells such as trophoblasts. This approach is preferred over surgical intervention in hemodynamically stable patients, as it reduces the risk of adhesions and preserves tubal function.

**Why Each Wrong Option is Incorrect**
**Option A:** Methamphetamine is a central nervous system stimulant with no role in the treatment of ectopic pregnancy.
**Option B:** Bromocriptine is a dopamine agonist used to treat prolactinomas and other conditions, but it is not indicated for ectopic pregnancy.
**Option C:** Clomiphene citrate is a selective estrogen receptor modulator (SERM) used to stimulate ovulation, but it is not used to treat ectopic pregnancy.

**Clinical Pearl / High-Yield Fact**
In patients with suspected ectopic pregnancy, the beta subunit of human chorionic gonadotropin (β-hCG) is typically elevated, but a plateau or decline in β-hCG levels after initial treatment with methotrexate is a good prognostic sign, indicating successful treatment.

**Correct Answer:** C. Methotrexate